1. Field of the Invention
The present invention relates to a silicon nitride member including a substrate formed through sintering of a silicon nitride material, and a hard film formed on the surface of the substrate, as well as to a method for manufacturing the same and to a cutting tool.
2. Description of the Related Art
Conventionally, in order to enhance wear resistance of a sintered member, such as a ceramic member, the surface of a substrate of, for example, a sintered silicon nitride member is coated with a hard film composed of hard components, such as TiCN.
Examples of the above-mentioned coating method include a CVD (chemical vapor deposition) process and a PVD (physical vapor deposition) process, in which hard components are deposited on the substrate surface to thereby form a hard film on the same.
When a sintered member coated with a hard film was used as, for example, a cutting tool, the cutting tool (a coated tool) exhibited significantly enhanced wear resistance.
In recent years, applications of a coated tool have been shifting toward heavy cutting, which involves a heavy cutting load. Under the circumstances, even a coated tool has been required to exhibit a certain level of resistance to chipping, in addition to high wear resistance.
According to the CVD process or the PVD process mentioned above, hard components are deposited at high temperature, thus involving the following problems: because of difference in coefficient of thermal expansion between the hard film and the substrate, stress remains in the substrate surface; and high temperature employed during deposition modifies the substrate surface. As a result, the strength of the substrate coated with the hard film is impaired as compared with that of the bare substrate.